Hi, this is a puzzle. I looked at the death record for John Grant in Canada and the informant on it is William Grant son of John. William says that John Grant's parents are John Grant & Catherine McEachren. These two are who you are saying the parents of Ann, Mary & Catherine are.
Looking about I found a marriage for a John Ferguson & Catherine McEachren on the 27 December 1875 Barony, Glasgow, Lanarkshire. In the 1881 Scotland census I found:
1881 census-Cambusnethan, Lanark
John Ferguson age 42 born 1839 Wishaw, Lanark occ: iron moulder
Catherine Ferguson age 36 born 1845 Shotts, Lanark
John Ferguson age 11 born 1870 Shotts, Lanark son
Ann Ferguson age 8 born 1873 Shotts, Lanark daughter
Catherine Ferguson age 4 born 1877 Shotts, Lanark daughter
Marion Ferguson age 9 months born 1880 Shotts, Lanark daughter
1891 census Cambusnethan, Lanark
Andrew Colquhoun age 53 born 1838 Tollcross, Lanark occ: iron moulder
John Ferguson age 21 born 1870 Shotts, Lanark occ: iron moulder son
Donald Ferguson age 7 born 1884 Shotts, Lanark son
Marion Ferguson age 10 born 1881 Shotts, Lanark daughter
Catherine McLean age 60 born 1831 Islay, Argyllshire housekeeper
** note the 3 children have Andrew Colquhoun listed as their father in the 1891 census
1891 census Scotland-Glasgow
Ann Ferguson age 19 born Glasgow occ: cleaner in the Glasgow Royal Infirmary
Catherine Ferguson age 14 born Glasgow occ: steam loom weaver listed as niece living with the McIntyres
If you look at the1901 Scotland census it says that Catherine was born in Islay, Argyllshire just as Catherine McLean was in 1891 census which leads me to believe that it is indeed Catherine in the 1891 census with her children. What I'm wondering is could John Ferguson have died sometime between William's birth in 1892 and 1901 and perhaps Catherine remarried to John Grant who adopted her children??? It seems odd that a. the children were born Ferguson & called Grant with same dad b. why would John Ferguson become John Grant after the children were born?? c. the places of birth & occupation is different between the 2 men which leads me to believe they are indeed 2 separate men. Hope this helps, Kim